1. Field of the Invention
The present invention relates to a microfluidic device for distributing a small amount of reagent in channels formed on chips to test the reagent. The present invention is used for, for example, gene amplification by a PCR method.
2. Description of the Related Art
Conventionally, Japanese Patent No. 3120466 proposes that a capillary is used as a channel for a reagent or a reaction solution for gene amplification by the PCR method.
More specifically, three vessels containing three liquids whose temperatures differ from one another are prepared. The three liquids are adjusted so as to be a heat denaturation temperature (95° C., for example), an annealing temperature (55° C., for example) and a polymerization temperature (75° C., for example), respectively. One capillary, which is separately prepared, is placed in a manner to soak sequentially in each of the three liquids. A reagent is injected into the capillary and the injected reagent is transported in the capillary using a gas supplied from end portions of the capillary. A three-way valve is switched to control a supply of the gas so that the reagent is provided sequentially in a position of each of the three liquids for each predetermined time interval. The repetition of this operation gives the reagent a temperature cycle.
In addition, another method is also proposed in which three large temperature portions having different temperatures are prepared, a meandering channel is formed to sequentially pass through the three temperature portions plural times and a reagent is transported unidirectionally within the channel.
Meanwhile, in recent years, a μ-TAS (Micro Total Analysis System) has drawn attention that uses a micromachining technique to microfabricate equipment for a chemical analysis or a chemical synthesis and then to perform the chemical analysis or the chemical synthesis in a microscale method. Compared to the conventional systems, a miniaturized μ-TAS has advantages in that required sample volume is small, reaction time is short, the amount of waste is small and others. The use of the μ-TAS in the medical field lessens the burden of patients by reducing volume of specimen such as blood, and lowers the cost of examination by reducing reagent volume. Further, the reduction of the specimen and reagent volume causes reaction time to shorten substantially, ensuring that examination efficiency is enhanced. Moreover, since the μ-TAS is superior in portability, it is expected to apply to broad fields including the medical field and an environmental analysis.
Japanese unexamined patent publication No. 2002-214241 discloses a technique in which such a μ-TAS is used to transport a reagent. According to the patent publication, two micropumps are used to transport two kinds of reagents which are subsequently joined together and the reagents after joining together are reciprocated within one channel after the confluence.
According to an apparatus described in Japanese Patent No. 3120466 mentioned above, the three-way valve is switched to control a supply of the gas, so that a movement amount of the reagent, i.e., a position of the reagent is controlled. Accordingly, positioning of the reagent is far from easy and it is difficult that the reagent is brought to a standstill at a predetermined position correctly and a temperature process using a liquid is performed precisely. In addition, the use of the three vessels and the capillary imposes limitation on reduction in the size of the apparatus. In other words, downsizing and improvement in portability are difficult.
Further, in the case where an apparatus has a meandering channel formed on a microchip and serves to transport a reagent unidirectionally, an amount of the reagent cannot be reduced and a pump is large. Accordingly, downsizing of the apparatus is far from easy.
When a micropump is used to transport a reagent, it is necessary to fill an area extending from the micropump to a portion for a temperature process with the reagent. Accordingly, it is impossible to reduce an amount of the reagent.